The present invention is directed to methods and devices for processing fluids in energy conservation and environmental pollution control applications using regenerative techniques.
Regenerative systems have long been used in energy conservation and environmental equipment. One of the best known examples of the use of a regenerative system in energy conservation is the use of regenerators in open-hearth steel furnaces. In such regenerators, two stationary beds of heat transfer and storage material are used. Dampers are provided at the inlet and outlet of each bed to alternately allow hot furnace exhaust gas and cold ambient air to flow through each bed. The heat in the hot exhaust air is therefore transferred to the colder heat-transfer material during the first part of the cycle. The ambient air then cools the hot heat-transfer material during the second part of the cycle. Thus the ambient air recovers heat which would otherwise be wasted from the hot furnace exhaust gas. Other examples are regenerators in blast-furnace stoves for the production of pig-iron and regenerator systems for by-product coke ovens which follow a similar operating principle. Another type of a regenerative heat-exchanger is the Ljungstrom wheel which is widely used in commercial HVAC and power plant applications. The standard design of the Ljungstrom wheel has a moving disc of heat transfer and storage material which is alternately moved between hot and cold air streams to transfer the heat from the hot air to the cold air Detailed description of these regenerative heat-exchanger systems is given in literature such as Perry""s Chemical Engineering Handbook, Fifth edition.
Another form of the regenerative heat-exchanger is described in the Steam Handbook by Babcock and Wilcox. It is similar to the Ljungstrom wheel but has a stationary wheel with revolving inlet and outlet plenums for the entry and exit of the hot gases and cold gases into the heat-exchanger core. Thus in this design, the heat transfer media remains stationary while the hot and cold air streams are moved through various sections of the heat-transfer media to transfer heat from the hot gases to the cold gases.
The regenerative heat-exchanger concept has been widely adopted for conserving energy in processes which clean polluted gas streams by oxidation of the pollutants in a furnace. Such equipment is commonly known as Regenerative Thermal Oxidizers. Currently two types of Regenerative Thermal Oxidizers are commercially available. The first type uses the principle of the regenerators as described above for steel furnace regenerators and is herein referred to as a dampered conventional Regenerative Thermal Oxidizer. Thus such Regenerative Thermal Oxidizers use at least two beds which contain regenerative heat-transfer materials. The hot oxidized cleaned air and the relatively colder polluted air is alternately passed through each bed to transfer the heat from the hot clean oxidized gas to the cold process gas. The second type of Regenerative Thermal Oxidizer uses the stationary bed principle of the Ljungstrom wheel as described in the Steam Handbook and is herein referred to as a rotary valve Regenerative Thermal Oxidizer. In this system, a plurality of beds containing heat-transfer materials are arranged in a radial manner. A rotating valve mechanism selectively allows the cold polluted air and the hot oxidized air to alternately pass through each bed to transfer heat from the hot air to the cold air.
Examples of conventional dampered Regenerative Thermal Oxidizers are described in U.S. Pat. Nos. 5,098,286 and 5,026,277 to York. Examples of the rotary valve Regenerative Thermal Oxidizers are described in U.S. Pat. No. 5,460,789 to Wilhelm, U.S. Pat. No. 5,016,547 to Thomason, and U.S. Pat. No. 4,280,416 to Edgerton.
Regenerative methods which use adsorption mechanisms and/or chemical reactions to effect the cleaning of polluted air streams have also been used in environmental control processes. A common example of such a regenerative method is the adsorption of Volatile Organic Compounds (VOCs) by granulated activated carbon (GAC) or specialized zeolites or specially modified resins. Such systems are generally used for concentrating very-low concentration VOC-containing process air-streams prior to their final recovery or disposal. Systems using granulated activated carbon generally operate using the bed principle while systems using zeolites generally use the Ljungstrom wheel principle. An example of a granulated activated carbon adsorption system is the multiple bed adsorption system sold by Calgon Corporation and other vendors. An example of the zeolite wheel adsorption system is the Ecopure(TM) system sold by Durr Environmental.
Regenerative techniques are also used with reversible chemical reactions. An example of a regenerative process which utilizes a reversible chemical reaction for cleaning polluted air is described in an article titled xe2x80x9cA Sorbent Regenerator Simulation Model in Copper Oxide Flue Gas Cleanup Processesxe2x80x9d published in Environmental Progress, volume 17, no.2. This article describes a method of using copper oxide for the simultaneous removal of sulfur oxides and nitrogen oxides from flue gas. In the initial step, the copper oxide reacts with sulfur dioxide and oxygen in the flue gas to form copper sulfate. The copper sulfate and the copper oxide then act as catalysts for the reduction of oxides of nitrogen by ammonia. The copper oxide is then regenerated by reduction with methane.
Each of the regenerative process configurations described above have inherent design, constructional and operational problems. For example, conventional dampered Regenerative Thermal Oxidizers require fast-acting dampers to minimize the direct bypassing of the polluted air to the atmosphere during the time-interval in which the regenerators"" control-damper blades are moving from an open to a closed position or vice-versa during the switching of the regenerator from the hot clean air to the cold polluted air or vice-versa. Fast acting dampers generally have severe maintenance problems especially on large units because the damper blade has to be moved rapidly. The inertia of the moving damper blade is difficult to control generally causing the damper blade to slam on the damper seals causing them to deteriorate rapidly. Thus frequent replacement of damper blades and seals is often required on such units. The inertia of the damper blades and the need for large quantities of motive fluids such as hydraulic fluid or compressed air to operate the dampers also requires that the dampers be opened and closed at long intervals. Thus short cycle times of less than a minute are difficult to achieve in such units which makes it difficult to reduce the quantity of the heat-transfer materials used in such heat-exchanger beds.
The problems of conventional dampered Regenerative Thermal Oxidizers are well described in the above-referenced prior patents for rotary valve Regenerative Thermal Oxidizers. While rotary valve Regenerative Thermal Oxidizers utilizing the Ljungstrom wheel principle have been used to try to overcome these problems, they suffer from cross-leakage and capacity limitations. The gaps between the moving and stationary parts of the heat-exchanger are difficult to seal because the beds generally have to be wedge-shaped to fit radially in a circular array within a cylindrical shell. Therefore, complicated radial, longitudinal, and peripheral sealing mechanisms, which require accurately machined parts, are needed to keep cross leakage of the polluted air from the oxidized air. Such sealing is difficult to achieve especially for the radial, longitudinal, and peripheral moving parts that exist within such units. Thus increased leakage of polluted air into the cleaned air occurs which reduces the destruction and removal efficiency of rotary valve Regenerative Thermal Oxidizers compared to conventional dampered Regenerative Thermal Oxidizers. Therefore rotary valve Regenerative Thermal Oxidizers generally have a lower Destruction and Removal Efficiency (DRE) than conventional dampered Regenerative Thermal Oxidizers. The large mass and inertia of the rotating valve mechanism in rotary valve Regenerative Thermal Oxidizers generally requires slow movement which makes it difficult to reduce the cycle time to less than one minute. Therefore, the use of rotary valves on Regenerative Thermal Oxidizers has generally not reduced the size of the heat-exchanger beds. Thus the cost-savings of such a unit are marginal compared to conventional dampered Regenerative Thermal Oxidizers. The use of a rotating mechanism in rotary valve Regenerative Thermal Oxidizers also requires that the regenerative beds be generally arranged in a circular array over the rotating valve mechanism. Thus the capacity of the rotary valve Regenerative Thermal Oxidizer is generally restricted by the maximum diameter of a cylindrical shell that can be economically fabricated and shipped. There is therefore a need for a Regenerative Thermal Oxidizer which combines the advantages of dampered Regenerative Thermal Oxidizers with the advantages of rotary valve Regenerative Thermal Oxidizers. Such a Regenerative Thermal Oxidizer would have a large number of mechanically switched regenerative beds as in the rotary valve units. However, such a Regenerative Thermal Oxidizer would be built in a rectangular configuration for economical fabrication and installation. Further, such a Regenerative Thermal Oxidizer would have a larger flow-capacity than currently achievable by rotary valve Regenerative Thermal Oxidizers. Finally, such a Regenerative Thermal Oxidizer would have seals that provide a very high VOC destruction and removal efficiency. Yet further, such a Regenerative Thermal Oxidizer would be capable of shorter cycle times than is possible with presently available regenerative bed switching mechanisms resulting in smaller and more economical regenerative heat-exchanger beds.
The problems described above with respect to dampered bed Regenerative Thermal Oxidizers and rotary valve Regenerative Thermal Oxidizers are also manifested in other regenerative devices such as granulated activated carbon and zeolite adsorbers which are generally known as VOC concentrators. For example, a carbon adsorber operates with a cycle time of at least an hour. It therefore requires a large volume of expensive granulated activated carbon to adsorb the VOCs. The large amount of carbon requires large quantities of steam or hot air for desorption of the adsorbed VOCs. A large amount of energy is wasted in operating such devices since only 10 percent of the energy is used for heating the bed during desorption; the remaining 90 percent of the energy in the desorbing steam is reportedly lost as vapor or is used for heating the bed and the vessel. Thus, the use of smaller cycle times and shorter beds is desirable in carbon adsorption units. Rotary carbon units attempt to reduce the cycle time in VOC Concentrators by using smaller quantities of adsorption material which is configured as a rotating bed. The mechanism used is generally similar to those found in stationary Ljungstrom wheel regenerative heat-exchangers wherein a disc shaped wheel is rotated between fixed radially oriented plenums. In some other configuration, the adsorption material is contained in baskets which are configured to form a hollow cylinder which rotates between longitudinally oriented plenums. However, these units also suffer from sealing problems similar to those described above for the rotary-valve Regenerative Thermal Oxidizers. The mass of the moving adsorption bed also makes it difficult to reduce the cycle time of the rotary adsorber which typically operates at about 1 to 3 revolution per hour. There is therefore a need for a regenerative adsorber which combines the advantages of dampered regenerative adsorbers with the advantages of rotary valve regenerative adsorbers. Such an adsorber would have a large number of mechanically switched regenerative adsorption beds as in the rotary valve absorbers Such an adsorber would be built in a rectangular configuration enabling economical fabrication and large flow-capacities. Further, such an adsorber would have seals that provide a very high VOC transfer efficiency. Yet further, such an adsorber would be capable of shorter cycle times than is possible with current switching mechanisms, resulting in smaller and more economical regenerative adsorption beds.
Therefore, it will be apparent from the above discussion that a need exists for a means of controlling the flow of air through individual regenerative beds used in Regenerative Heat-Exchangers, Regenerative Thermal Oxidizers, Regenerative Catalytic Oxidizers, Regenerative VOC Concentrators, and Reversible Chemical Reactors without the disadvantages inherent with the rotary valve arrangement while retaining the advantages of relatively high destruction, transfer or conversion efficiencies, easy installation, and relatively large flow capacities of conventional dampered bed regenerative systems.
The present invention provides these advantages through the use of a novel Multi-Port Valve Assembly which can be used with various regenerative system such as heat-exchangers, VOC Concentrators, chemical reactors, thermal oxidizers, and catalytic oxidizers.
It is well known to use multi-port valves to selectively control the flow of fluids through selected ports. An example of a multi-port valve for diverting gas flow through various ports is described in U.S. Pat. No. 4,576,201 to Guggenheim. This valve uses a stainless-steel endless belt with apertures at pre-determined positions to selectively switch on or switch off the flow of fluids through various ports. However, the use of such valves with regenerative systems is not known.
A specially designed Multi-Port Valve Assembly is used herein with regenerative systems. The Multi-Port Valve Assembly according to the principles of the invention can be used with various embodiments of regenerative systems. For example, the Multi-Port Valve Assembly can be used with single-bed as well as multiple-bed regenerative systems. More than one Multi-Port Valve Assembly can also be used in a regenerative system to accomplish the specific requirements of the system.
A first embodiment of the regenerative system comprises a regenerative device and a Multi-Port Valve Assembly. In this system, the Multi-Port Valve Assembly has a rigid flow control means which controls the flow of the process fluid through a single regenerative device. The flow control means has fluid passage zones which are movingly overlapped with the fluid inlet port of the regenerative device to open or close the fluid inlet ports. Thus the flow of the process fluid through the single regenerative device is selectively switched on or off to accomplish the regenerative process. In another single regenerative device embodiment of the regenerative system, the flow control means is a flexible belt, the ends of which are dropped in to take up wells. In yet another single regenerative device embodiment of the regenerative system, the flow control means is a flexible belt, the ends of which are spooled on spool drums at either end. In a further embodiment, the flow control member is a flexible endless belt which travels in an endless loop to open and close the fluid inlet port to the regenerative device.
In another embodiment of the regenerative system, the Multi-Port Valve Assembly has a flow control means which is configured as an endless belt and which controls the flow of two process fluids through a single regenerative device. In another embodiment of the regenerative system, the Multi-Port Valve Assembly has a flow control means which is configured as an endless belt and which controls the flow of two process fluids through two regenerative devices. In yet another embodiment of the regenerative system, the Multi-Port Valve Assembly has a flow control means which is configured as an endless belt and which controls the flow of three process fluids through six regenerative devices. This embodiment is described as an example of the general principles of the invention embodied in a regenerative system which can be used with any number of process fluids and any number of regenerative devices.
In a further embodiment of the regenerative system, two Multi-Port Valve assemblies are used, one on each end of the regenerative devices, to control the flow of the process fluids through the regenerative devices. The Multi-Port Valve Assemblies can be configured so that the process fluids can flow either in a parallel-flow mode or a counter-flow mode within the regenerative devices. This regenerative system is particularly useful as a regenerative heat-exchanger or a VOC Concentrator. A further embodiment of the above system uses energy transfer devices within the regenerative material in the regenerative devices for use of the regenerative system as a Regenerative Thermal Oxidizer or a Reversible Chemical Reactor.
Yet another modification of the above embodiment further incorporates catalysts within the regenerative materials for use of the system as a Regenerative Catalytic Oxidizer. Yet another embodiment of the above described regenerative system uses a common flow control member to service both Multi-Port Valve Assemblies. A further embodiment of the above regenerative system uses a common drive mechanism to move the two flow control members of the two Multi-Port Valve Assemblies.
A different embodiment of the regenerative system incorporates a common combustion chamber at the second end of the regenerative devices for use of the system as a Regenerative Thermal Oxidizer. A variation of this embodiment further incorporates catalysts within the regenerative materials for use of the system as a Regenerative Catalytic Oxidizer.
The flow control means used in the above described embodiments can be made of metallic or non-metallic materials. Further the flow control means can be configured as a single layered belt or a composite belt made of multiple layer of different materials. The fluid passage zones on the flow control means can be configured as orifices or slots or other suitable shapes. The fluid passage zones can be arranged so the specific requirements of the regenerative system can be satisfied.
The use of the Multi-Port Valve Assembly described herein with regenerative systems eliminates the control dampers and associated hardware and instrumentation that is required with conventional dampered regenerative systems which use control dampers for reversing the flow of the process fluid through the regenerative beds of such systems. It also reduces the process disturbances caused by pressure surges that occur with conventional dampered regenerative systems. Furthermore, the use of the Multi-Port Valve Assembly provides for a larger flow-capacity compared to currently available rotary-valve regenerative systems because the regenerative beds can be designed with a rectangular cross-section. Therefore, the size of the regenerative beds in such systems is not restricted by the fabrication and shipping limitations of cylindrical shaped vessels. The use of the Multi-Port Valve Assembly reduces the complexity of the regenerative system by eliminating the complicated control system and the hydraulic or compressed-air systems required to move the control dampers. Thus a regenerative system which uses a Multi-Port Valve Assembly can be easily maintained by the average maintenance technician. The use of the Multi-Port Valve Assembly makes the regenerative system easier to fabricate without the need for very high-tolerance machined parts or complicated seals to reduce the cross-leakage that is sometimes inherent in such systems.
Still further advantages of the invention will be apparent from the following drawings and description.